/**
 * 
 */
package com.socialnetwork.security.pwd;

/**
 * @author asoundar
 *
 */
public class Base64 {
	
	public static final char PLUS = '+';
	public static final char QUESTION = '?';
	public static final char FORWARD_SLASH = '/';
	public static final char EQUAL = '=';
	
	protected static char getChar(int sixbit) {
		if (sixbit >= 0 && sixbit <= 25) {
			return (char)(65 + sixbit);
		}

		if (sixbit >= 26 && sixbit <= 51) {
			return (char)(97 + (sixbit - 26));
		}

		if (sixbit >= 52 && sixbit <= 61) {
			return (char)(48 + (sixbit - 52));
		}

		if (sixbit == 62) {
			return PLUS;
		}

		return sixbit != 63 ? QUESTION : FORWARD_SLASH;
	}

	public static String encode(byte raw[]) {
		return encode(raw, 0, raw.length);
	}
	
	public static String encode(byte raw[], int offset, int length) {
		int lastIndex = Math.min(raw.length, offset + length);

		StringBuilder sb = new StringBuilder(
			((lastIndex - offset) / 3 + 1) * 4);

		for (int i = offset; i < lastIndex; i += 3) {
			sb.append(encodeBlock(raw, i, lastIndex));
		}

		return sb.toString();
	}
	
	protected static char[] encodeBlock(byte raw[], int offset, int lastIndex) {
		int block = 0;
		int slack = lastIndex - offset - 1;
		int end = slack < 2 ? slack : 2;

		for (int i = 0; i <= end; i++) {
			byte b = raw[offset + i];

			int neuter = b >= 0 ? ((int) (b)) : b + 256;
			block += neuter << 8 * (2 - i);
		}

		char base64[] = new char[4];

		for (int i = 0; i < 4; i++) {
			int sixbit = block >>> 6 * (3 - i) & 0x3f;
			base64[i] = getChar(sixbit);
		}

		if (slack < 1) {
			base64[2] = EQUAL;
		}

		if (slack < 2) {
			base64[3] = EQUAL;
		}

		return base64;
	}	
}
